The octoplex can be a lonely place when a slightly underwhelming summer season is winding down. At times like these, discovering a hidden little film gem is like finding a cool, late-season breeze.

For a certain slice of the audience demographic, the low-budget slasher flick “You’re Next” is one such flick — well-crafted, way bloody, often raw and shocking, with just the right amount of inside snark.

Stuffed wall to wall with people who are far from household names, it’s the kind of film that restores your faith in B-movie schlock.

Director Adam Wingard and writer Simon Barrett, who have worked on a number of low-budget slasher flicks together and separately, are certainly not plowing new ground here; they are well-schooled in the often rigid expectations and conventions of this subgenre and stick mainly to the script.

But they do add a number of oddly quirky grace notes that spice up the party and make for those great mass audience reactions.

The film introduces us to the Davison family, a rich bunch with a Tudor-style mansion tucked way back in the woods. Dad (Rob Moran) is a folksy but uptight sort whose riches are never quite fully explained. Mom (Barbara Crampton) is spacey, with a fondness for drink and painkillers.

To celebrate their parents’ 35th wedding anniversary, their four children are coming to stay at the isolated mansion for a weekend: brothers Crispin (A.J. Bowen), Drake (Joe Swanberg) and Felix (Nicholas Tucci), and their little sister Aimee (Amy Seimetz). Oh, and each of the kids has brought along a significant other, the strangest of whom is Felix’s squeeze, Zee (Wendy Glenn), a spooky Goth girl.

So, that’s 10 victims ripe for slaughter! And it doesn’t take long for the resident psychos to show up in the woods outside, firing steel arrows through the windows at the terrified family. Their signature touch: They all wear plastic animal masks while hacking and slashing.

It’s a pretty one-sided fight for a while, highlighted by a scene in which one family member goes barreling out the front door of the mansion at a full run and heads straight into a wire strung across the entrance that goes through her throat like butter.

Then someone on the family’s side starts stepping up, making common-sense suggestions on strategy and fortifications that come to prove surprisingly effective. I won’t say who it is, but I can’t resist sharing the explanation for the character’s abilities: a childhood spent in a survivalist camp.

The arterial blood sprays in grand, nihilistic jets as the battle swings back and forth, eventually acquiring new wrinkles about two-thirds of the way in that turn things into a twisted little dysfunctional family morality play.

It’s topped by Crispin delivering one of the most intentionally funny speeches in horror movie history, a touch of action that owes a little something to the ending of the original “Night of the Living Dead” and a final sight gag involving a weighted ax rigged above a doorway in ridiculous but deadly Rube Goldberg fashion.

Accomplishing its grisly task in just over an hour and a half, “You’re Next” proves to be a blood-pumping diversion.